I used a RenPy save editor (I used this after googling it) to change the value of nia_alert00 to 0, and the issue was solved.
As long as you can find the save file (.../game/saves/PAGE-SLOT-LT1.save), I assume it would be the same process.
The one you linked didn't seem to work but editing that value with this one did! https://saveeditor.online/
Thanks so much for the heads up!